The long-term goal of this project is to discover drugs that will protect normal cells from cancer chemotherapy. The oncogene ras is present in approximately 30 percent of human tumors: a normal non-oncogenic ras is found in normal cells. This normal ras (but not oncogenic ras) can be switched off by the cytosolic protein GAP resulting in inhibition of cell division. This difference can be exploited by compounds that act through GAP-ras to inhibit the proliferation of normal cells, sparing them from the effects of anti- proliferative therapy. Most previous work on GAP-ras interactions has utilized soluble ras. Since lipids appear to regulate the GAP-ras interaction, it is important to use the more physiological membrane-bound form of ras p21. In Phase I of this SBIR grant, an assay will be constructed for membrane-bound non- oncogenic ras protein and its regulation by GAP (Specific Aim 1). The membrane-bound ras will then be used to study the effects of regulatory lipids (Specific Aim 2). Subsequent to Phase I, compounds acting to inhibit normal ras function will be identified, and tested in relevant cell and animal models.